Manually powered impact type stapling and tacking machines are well known. Such devices generally comprise a housing, an energy storage spring, a fastener feeding system, a movable operating handle to deflect the energy storage spring, a mechanism to rapidly disengage the handle from the deflected spring, and a sliding plunger linked to the spring to impact and drive a fastener from the housing. Examples of such impact type stapling machines are disclosed in Krantz U.S. Pat. No. 2,326,540, Abrams U.S. Pat. No. 2,671,215, Libert U.S. Pat. No. 2,769,174, Males et al U.S. Pat. No. 3,610,505, and Fealey U.S. Pat. No. 4,452,388.
In the impact stapler of Marks U.S. Pat. No. 5,165,587, an upper lever pivotally mounted toward the rear of the stapler housing is depressed to actuate a pivotally mounted lower lever for raising a striker against the bias of an actuator coil spring engaging the rear of the lower lever. After the striker is raised, a linkage which connects the upper lever to the lower lever is disengaged to release the lower lever for actuation by the coil spring which drives the striker downward to eject a fastener from the stapler housing. The linkage is re-engaged when the operating handle is released and returned to its rest position prior to the next power stroke.
In the impact stapler of co-pending U.S. application Ser. No. 08/074,941, filed Jun. 10, 1993, an upper lever is pivotally mounted toward the rear of the stapler housing and is coupled by a pin and slot connection to a lower lever pivotally mounted on the stapler housing. An actuator leaf spring is coupled to a staple striker at the front of the housing. When the upper lever is depressed to pivot the lower lever, a tab on the striker is engaged by the front tip of the lower lever and the striker is raised against the bias of the leaf spring. When the striker is raised to the top of its power stroke, the lower lever is shifted by a camming action on its front tip in a first lateral direction to position the front tip to one side of the striker tab and to release the striker which is driven downward by the leaf spring to eject a staple from the stapler housing. When the upper lever is released, the lower lever is shifted in a second lateral direction by a return spring acting on a rear portion of the lower lever to position the front tip on the opposite side of the striker tab. The lower lever is pivoted to its rest position by the return spring which engages a cam on the stapler housing and shifts the lower lever in the first lateral direction to position the front tip underneath the striker tab for the next power stroke.
The present invention provides an improved fastening device of the type disclosed in the copending U.S. application Ser. No. 08/074,941 including an improved actuator mechanism with a reset device which eliminates the need for using the return spring to perform the dual function of shifting the lower lever laterally in one direction after the striker is driven downward and shifting the lower lever laterally in the opposite direction for engagement with the striker tab when the lower lever is returned to its rest position. Also, the invention provides an improved actuator mechanism including a lateral positioning feature for accurately locating the lower lever in a predetermined lateral position relative to the striker tab.